And matthew exbbidge dun



s it. 6, 1932.

c. e. suns ET AL MOISTURE INDICATINQ INSTRUMENT FOR WOOD Filed May 16, 1930 A ORNEY F/GU/PE 3 INVENTO FIGURE 1 I 4 NW! Patented Sept. 6, 1932 UNITED STATES PATENT OFFICE CHLUNCEY GIIY SUITS, OF SGHENECTADY, NEW YORK, AND MATTHEW ELBBIDGE DUN- LAP, OI MADISON, WISCONSIN, DEDICATED THE FREE USE 01' THE GOVEBN- KENT AND THE PUBLIC MOISTURE INDICATING INSTRUMENT F63 WOOD Application filed HayJG, 1930. Serial No. 458,088.

(GRANTED UNDER THE ACT OF IAROE 8, 1883, AS LIENDED APRIL 80, 1888; 870 0. G. 757) This application is made under act of March 3, 1883, chapter 143 (22 Stat. 625), as amended April 30, 1928; 370 O. G. 757 and the invention herein described and claimed may be manufactured and used by or for the Government for governmental purposes w1thout the payment of any royalty thereon.

Our invention relates to a new and improved moisture indicating instrument particularly for-wood or other more or less dense fibrous or baled materials.

It has been established experimentally that the electrical resistance of wood is a function of its moisture content and that this characteristic is great compared to other propertles such as density, extractives, ash content, and the like.

The greater portion of wood used 1s dried either in the air or in kilns before it is used go and it is of considerable importance to the user or shipper of lumber to know the moisture content of the lumber before use or shipment.

It is the purpose of this apparatus to provide a means of measuring the moisture conac tent of wood instantaneously and which is comparatively small, simple in constructionand operation and economical. I

We attain this object by means of the device illustrated in the accompanying drawing in :0 which- Figure 1 is a dia ammatic view of the w 1ring used in the fun amental electrical circuit; Figure 2 is a diagrammatic new of the wlring used in a more convenient form; Figure 3 1s a side elevation of the hammer-like implement; and Figure 4 is a top plan view of the same.

The basis of the new instrument is the two element neon tube. This tube contains no filament or hot cathode but consists of two identical electrodes sealed in a glass tube which has been evacuated and filled with neon gas at a pressure of a few microns of mercury.

l The most important characteristic of the device is the current-voltage relation. When the potential difference between the two electrodes is continuously increased no current will flow until a certain minimum potential is obtained, where the current will rise almost immediately to a pointat which a glow disthe condenser 2- starts to discharge.

charge will takeplace. Any increase in voltage will now result in a linear increase in current. However, if the potential is decreased to a certain point it will be found that current will flow until some smaller alue and its corresponding potential are reached, when the glow and current suddenly drop to zero.

The properties of this tube can be utilized 1n a very unique manner as indicated in the fundamental circuit shown in F i ure 1 in which, 1 is a two electrode neon giwlamp, 2 a variable condenser, 3 the resistance to be measured, 4 a battery to supply the current, and 5 a switch to open and close the circuit.

When the switch 5 is closed the condenser 2 is charged through the resistance 3 until the ionization voltage of the neon tubeis reached when the latter breaks down and presents a low impedance path through which This discharge, accompanied by the characteristic glow, proceeds until the condenser voltage has dropped to a somewhat lower value. At this minimum voltage the tube ceases to be conducting, the condenser 2again charges up to the neontube discharge point and the cycle described repeats itself. Thus the circuit functions as an oscillator at a frequency determined by the values of the resistance 3, condenser 2, the battery voltage and the properties of the neon glow lamp.

In this way when a constant voltage is maintained the fre uency of the oscillations may be altered by e1ther changing resistance 3 or capacity 2 in the circuit. Since the resistance is the variable to-be measured the proper condenser may be turned into the circuit and the oscillations counted in a unit of time and thus correlated with moisture content of the wood under test.

A more convenient form is shown in Figure 2. In this case an additional neon tube 6, condenser 7, and resistance 8 have been added. These are so arranged that .when the switch is turned on the oscillations as indicated by the glow in the neon tube occur at the rate of approximately per minute and this part of the circuit may be referred to as the standard.

Again referring to Figure 2, a common battery 9' is used to supply the current, a switch 10 is used to open and close both circuits.

j- A group of condensers 11 to 28 are so pro portioned in sizethat when a piece of wood of a 'ven moisture content is attached to the ectrode 29 the selector maybe turned to one of the condensers and the oscillations 'of the test neon tube will be approximately the same 'as for the standard lamp 6. In this way the moisture content of wood may be determined from approximately 8 per cent to about 26. per cent. The contacts 32 are shown in Figure 2 as well as the calibration 33 in per cent moisture content and are used as a matter of convenience instead of an expression in terms of actual resistance.

'In carrying out this invention we have found that in the case of the standard circuit containing neon tube 6, condenser 7, and resistance 8 and a voltage of approximately 180 supplied by B type dry cells that a condenser of about 0.25 microfarads and a resistance of 4 megohms give satisfactory re sults. In the case of Douglas fir condensers having the following values have been found satisfactory. No condenser is necessary in the case of the 8 per cent stop as the capacity of the tube electrodes is approximately correct.

The fi res given above'are approximately correct or most of our native species but more particularly for Douglas fir.

Some modification of these values is necessary when accurate work is required on other species of wood. However, it is not intended that 26 per cent moisture content is as high as can be measured by this method as it is obvious that the range of the instrument may be increased by the use of a somewhat lower voltage or by the use of larger condensers.

The electrodes for this device are shown in Figure 3 and are mounted in a specially constructed hammer-like implement. It consists of a head 35, composed of two airs of plates 36 separated by an insulatin ody 37 of bakelite. The head is held to et er by bo1ts38 passing through the head ut insulated from the plates by bakelite washers 39.

Contact points 40 are provided at each end of the head 35 and are held in place by clamp screws 41 and plates 42. The wires 34 are connected to opposite plates and to the terminals 29 shown in Figure 2. Contact is made llzy driving the needle points 40 into-the wood. eedle points are provided on both ends of the hammer so that if one set is broken the other end may be used without delay. The

head is mounted on a suitable handle 43 which has been drilled'for the passage of the cable 44.

The apparatus ma be used in two ways, either as a sorter or or measuring moisture content. In case the instrument is to be used as a sorter to remove boards above a designated moisture content the following procedure is used: The selector 30 isset at the desired moisture content which is to serve as a dividing line and the electrodes 40 driven into the wood. If the test tube 31 oscillates faster than the standard the board has a higher moisture content than is desired and is discarded. On the other hand if the oscillations are equal to or less in number for the test tube 31 than for the standard tube 6 the board is considered satisfactory for use.

If it is desired to measure the moisture content of a piece of lumber the electrodes 40 are driven into the wood and the selector 30 turned across the contact points until the oscillations of the standard tube 6 and test tube 31 are approximately the same. The graduations 33 may be read and the moisture content obtained in this way.

The current drain is so small that the life of the batteries is practically their shelf life which insures economy in the use of the instrument. The instrument is extremely simple in construction and operation.

Having thus described our invention, we claim:

1. A moisture indicating instrument for wood comprising two dependent electrical circuits having a common battery; one circuit, lmown as the standard, includes a fixed resistance and a fixed condenser connected electrically in series and with a neon glow lamp shunted around the condenser in such a way that the neon glow lampwill flash at a fixed or standard rate per minute; and the other, a secondary or test circuit contains a fixed condenser, the capacity of which is definitely related to a certain moisture content of wood and with a neon low lamp shunted around it and connected electrically in series with electrodes capable of being driven into 2. A moisture indicating instrument for.

wood comprising two dependent circuits having a common battery; one circuit, known as the standard, includes a fixed resistance and a fixed condenser connected electrically in series, and a neon glow lamp shunted around the condenser in such a way that the neon glow lamp will flash at a fixed or standard rate per minute; and the other circuit, a secondary or test circuit, contains a group of fixed condensers, the capacity of each being definitely related to a certain moisture content of wood and so arranged that any one of them may be switched into the circuit; and a neon glow lamp shunted around said group of condensers and connected electrically in series with electrodes capable of being driven into the wood; thereby forming the resistance to be evaluated whereby the moisture content of the wood under test will be approximately equivalent to that represented by the condenser used in the standard circuit, when the neon tuhes in the two respective circuits flash at approximately the same rate.

3. A moisture indicating instrument for wood comprising two dependent circuits having a common battery: one circuit, known as the standard, includes a fixed resistance and a fixed condenser connected electrically in series: and a neon glow lamp shunted around said condenser in such a way that the neon glow lamp will flash at a fixed or standard rate per minute: and the other circuit, a secondary or test circuit, contains a group of fixed condensers, the capacity of each being definitely re ated to a certain moisture content of w and so arranged that any one of them may be switched into the circuit; and a neon glow lamp shunted around said group of condensers and con nected electrically in series with electrodes mounted in the faces of a hammer-like implement to facilitate driving contact points and removing them from the wood; thereby forming the resistance to be evaluated; whereby the moisture content of the wood under test will be a proximately equivalent to that re resented y the condenser used in g V the stan ard circuit when the neon glow lamps in the two respective circuits flash at approximately the same rate.

I 4. An electrical device for indicating the moisture content of fibrous materials comprising a source of-uni-directional electromotive force, energizing in parallel two in dependent electrical circuits for producing pulsation or relaxation type oscillations; the rstof said circuits comprising a resistance in series with a branch circuit of capacitance shunt connected to a gaseous discharge device in such a manner that a substantially constant rate of flashing of said discharge device occurs; the second of said circuits having similar electrical dimensions and properties but including the sample of fibrous material between test or probe electrodes as a resistance which depends upon the moisture content of said material in a known manner.

5. An instrument for indicating the moisture content of fibrous materials, comprising in combination a source of electromotive energy, energizing in parallel two independent circuits for producing electrical pulsations; the first circuit of said combination, pulsating at a fixed rate, for comparison to the pulsation frequency of the second or test circuit, which frequency is determined by the amount of moisture content. of the fibrous material under test, which material is incorporated in said test circuit by the application of probe electrodes which make intimate contact with the material being tested, comparison of the pulsation frequencies thus furnishing a criterion for the selection of specimens of the tested material above and below a specified moisture content.

6. A device for the measurement of moisture content in wood comprising a source of uni-directional electromotive force energizing in parallel two circuits a and b; circuit a comprising a resistance and capacitance in series relation and including a gaseous glow discharge device in shunt to said capacitance in such a manner that intermittent flashing of said discharge device takes place at a submoisture content of the wood in a known manner, may by change in capacitance be brought into substantial agreement with the flashing rate of similar discharge device of circuit a, thereby providing means for the measurement of said moisture content by the correlation of known moisture content with values of variable capacitance for similar flashing rates.

CHAUNCEY GUY SUITS. MATTHEW ELBRIDGE DUNLAP. 

